1. Field of the Invention
The present invention relates to a liquid applying apparatus and a liquid applying mechanism that applies a liquid to a print medium to be printed by an ink jet printing apparatus, and specifically, to control of a liquid supply mechanism which is included in the liquid applying mechanism and which supplies the liquid.
2. Description of the Related Art
Spin coaters, roll coaters, bar coaters, and die coaters are known as methods of applying a liquid or a liquid material on common media. These applying methods are based on consecutive application of a liquid to relatively elongate applying media. Thus, for example, if applying media of a relatively small size are intermittently conveyed and then a liquid is applied to the applying media, application beads may disadvantageously be displaced at a application start or end position for each applying medium. Thus, for example, resulting coats may be prevented from being uniform.
A configuration described in Japanese Patent Laid-Open No. 2001-070858 is known to solve these problems. This configuration is based on a die coater method, and uses a rotating rod bar. A coating compound is ejected through an ejection slit to form a coat on the rod bar. As the rod bar rotates, the coat formed comes into contact with an applying medium and is thus transferred to the applying medium. In this case, when the coat formed by the rod bar is not transferred or applied to the applying medium, the rotation of the rod bar allows the coating compound to be returned to and collected in a head via a collecting slit. That is, while the coating compound is not being applied, the rod bar continues to rotate, with the coating compound forming the coat on the rod bar. Thus, even if the applying media are discontinuously supplied and the coating compound is discontinuously applied to the supplied applying media, uniform coats can be obtained.
In the field of ink jet printing apparatuses, some known apparatuses use liquid applying mechanisms. Japanese Patent Laid-Open No. 2002-517341 describes the use of a doctor blade that contacts a roller. A coating liquid is collected between the blade and the roller so that the coating liquid is applied to the roller as the roller rotates. As the roller rotates, the coating liquid applied to the roller is transferred and applied to a support conveyed between the roller and another roller. Japanese Patent Laid-Open No. H08-072227 (1996) discloses a mechanism in an ink jet printing apparatus which similarly applies a processing liquid that insolubilizes a dye, before printing. In Embodiment 1 in Japanese Patent Laid-Open No. H08-072227 (1996), the processing liquid in a refilling tank attaches to a rotating roller and is thus pumped out. At the same time, the pumped-out processing liquid is applied to a print sheet.
In all of the configurations described in Japanese Patent Laid-Open Nos. 2001-070858, 2002-517341, and H08-072227 (1996), as the rod bar or the roller rotates, the applying liquid is applied or supplied to a surface of the bar or the roller. Consequently, the portion of the bar or roller to which the applying liquid is applied or supplied is open to or communicates with atmosphere. Thus, disadvantageously, the applying liquid may be evaporated, or when the posture of the apparatus is changed, the applying liquid may leak.
In particular, for the ink jet printing apparatus such as a printer, when the apparatus is miniaturized, applying the applying mechanisms described in Japanese Patent Laid-Open Nos. 2001-070858, 2002-517341, and H08-072227 (1996) to the apparatus is difficult in view of the leakage of the liquid which may occur when the posture of the apparatus is changed during transportation.
In contrast, Japanese Patent Laid-Open No. 2005-254229 discloses a configuration that seals the portion of the roller to which the applying liquid is applied or supplied. The configuration uses an ink chamber with an integral member located along a peripheral surface of the roller. The ink chamber is allowed to abut against the peripheral surface of the roller to form a liquid chamber between the ink chamber and the roller. Then, the roller is rotated to apply or supply the applying liquid in the liquid chamber to the roller.
Furthermore, as means for supplying the applying liquid to the mechanism applying the applying liquid based on a closed space as disclosed in Japanese Patent Laid-Open No. 2005-254229, two channels are used to couple the applying mechanism applying the applying liquid to applying liquid storing means for storing the applying liquid to form a circuit through which the applying liquid is circulated using a pump. As a specific example, Japanese Patent Laid-Open No. 2005-254229 discloses a configuration in which the pump is located on a downstream side of the applying mechanism in the circuit for circulation. This configuration sets the internal pressure of the applying mechanism to at most the atmospheric pressure. As a result, the possible leakage of the liquid from the applying mechanism can be prevented.
Moreover, according to the Japanese Patent Laid-Open No. 2005-254229, an on-off valve that switches between communication with the atmosphere and communication with the applying liquid storing means is located on an upstream side of a liquid applying space. Thus, the applying liquid in liquid holding section can be collected into the applying liquid storing means.
The applying liquid and air entrained in the applying liquid during an applying operation and air sucked during a collecting operation flow from the applying means into the applying liquid storing means via the channels. The applying liquid with no air entrained therein needs to be fed from the applying liquid storing means to the applying means. However, in the applying liquid storing means, the inflow air and liquid are separated from each other in a vertical direction. The liquid is then fed to the channel communicating with the liquid applying means, through an opening located in the vicinity of the bottom of the liquid applying means. Thus, air can be prevented from being entrained in the liquid supplied to the liquid holding section. Furthermore, to prevent the air flowing into the liquid storing means from being built up to increase the internal pressure of the applying liquid storing means, the applying liquid storing means includes a mechanism that enables communication with the atmosphere. The mechanism enabling the communication with the atmosphere is composed of an atmosphere communication port and an atmosphere communication valve that opens and closes the atmosphere communication port. This enables the liquid storing means to communicate with the atmosphere during the circulation and to be shut off from the atmosphere while the apparatus is not in use.
Thus, the liquid applying apparatus disclosed in Japanese Patent Laid-Open No. 2005-254229 can prevent the possible leakage of the applying liquid while the apparatus is not in use, for example, during transportation, based on the operation of collecting the liquid from the liquid holding section as well as the atmosphere communication valve, which enables the liquid storing means to be shut off from the atmosphere. The collecting operation and the mechanism shutting off the liquid storing means from the atmosphere enable prevention of the possible leakage of the applying liquid while the apparatus is not in use, for example, during transportation.
Additionally, in Japanese Patent Laid-Open No. 2006-338100, the mechanism provided in the applying liquid storing means and communicating with the atmosphere is positioned almost at the center of gravity of the applying liquid storing means. Thus, even with a change in the posture of the apparatus that is not in use or a change in environments such as the temperature of outside air, the possible leakage of the applying liquid can be prevented.
In contrast, Japanese Patent Laid-Open No. H06-178957 (1994) proposes that viscosity measuring means and viscosity control means for the applying liquid be provided to appropriately control the viscosity of the applying liquid.
However, the techniques disclosed in the above described patent documents pose the following problems.
The techniques described in Japanese Patent Laid-Open Nos. 2001-070858, 2002-517341, H08-072227 (1996), 2005-254229, and 2006-338100 fail to detect the condition of the applying liquid, for example, thickening or solidification of the liquid resulting from a temporal or environmental change, or a failure to supply the liquid to the applying mechanism. Thus, the applying operation may be performed with the applying liquid thickened or solidified or with the liquid failing to be sufficiently supplied to the applying mechanism. As a result, the applying liquid may be improperly applied to the medium. Furthermore, if the applying operation is continuously performed with the liquid failing to be supplied to the applying mechanism, the applying roller or related components contacting the applying roller may be excessively worn away. As a result, replacement of parts of the apparatus and maintenance of the apparatus may require much time and cost.
To deal with this problem, a viscometer for the applying liquid may be provided as disclosed in Japanese Patent Laid-Open No. H06-178957 (1994) so as to perform control such that, for example, the apparatus is stopped if the applying liquid is too viscous. However, this poses a new problem; the addition of viscosity sensing means and the viscosity control means increases the costs of the apparatus.